On Wed, 31 Aug 2005, Andy Dalton wrote: > Greetings, > > I'm attempting to connect five FTDI serial devices (FT232BM) to my > Linux system (2.6.13) via a 7-port USB hub. I am able to connect and > communicate with up to three devices successfully (one device at a > time). > > Adding additional devices cause problems. In the scenario I've > captured here, adding the fourth device causes intermittent > communications failures. When attempting to add the fifth device, the > device does not get recognized. Other times, I've gotten similar, but > different results with more than three devices. > > The hub is connected to the system via a 15' USB cable, and each > device is connected to the hub via 15' USB cables. > > Any ideas you might have would be appreciated. Are the cables too > long? Am I expecting too much by connected so many of these devices > to a single hub? Do I need a better USB controller? Do I need a > better USB hub? Is there some practical limit to the number of > devices I should expect to be able to attach at a given time?
It's possible that the cable length could cause problems; you're running up against the limits of the USB spec there. More likely your problem comes from plugging full-speed devices into a hub running at high speed. Try "rmmod ehci-hcd" so that everything is forced to run at full speed, and see if that helps. Alan Stern ------------------------------------------------------- SF.Net email is Sponsored by the Better Software Conference & EXPO September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
